Multiphoton photochemical processes generally involve the simultaneous absorption of two or more photons by an absorbing chromophore. In such processes, the chromophore typically does not absorb at the wavelength of the individual photons, but at sufficiently high intensity a simultaneous absorption of multiple photons by the chromophore occurs. For example, simultaneous absorption of two photons having a wavelength of λ has the effect of absorption of a single photon of wavelength λ/2. Whereas single-photon absorption generally scales linearly with the intensity of the incident radiation, two-photon absorption scales quadratically, and higher-order absorptions scale with a corresponding higher-order power of the intensity of the incident radiation. As a result, it is typically possible to perform multiphoton curing processes with three-dimensional spatial resolution. Furthermore, since the incident radiation is not attenuated by single-photon absorption within a reactive matrix or material, it is generally possible to selectively excite molecules at a greater depth within a material than would be possible via single-photon excitation.
Multiphoton induced photopolymerization, typically using a laser, has been used to fabricate three-dimensional devices with sub-micron resolution. Multiphoton fabrication has been used to manufacture mechanical and optical devices, such as cantilevers, gears, shafts, and microlenses.